A fuel pump having a pump function of sucking and discharging fuel in a fuel tank has been widely applied to a fuel supply device and a fuel supply control system. For example, in the fuel supply device, the fuel to be filtered by a filter element in a filter casing in a fuel filter is discharged from the fuel pump before the fuel is filtered, whereby a filtering efficiency can be increased. Further, in the fuel supply control system, the fuel pump is controlled by a control system, whereby a discharge pressure of the fuel can be correctly regulated.
A pump disclosed as a kind of fuel pump like this in Patent Document 1 exerts a pump function and a detection function, thereby detecting a capacitance according to a fuel property in the fuel tank such as an alcohol concentration. Here, in the fuel pump disclosed in Patent Document 1, a fuel property detection device to detect a capacitance correlated to the fuel property forms a gap to give the capacitance between a pair of detection electrodes arranged in a double cylindrical shape.